1. Field of the Invention
This invention generally relates to a wavelength division multiplexing (WDM) coupler, and more particularly to a WDM coupler which is adjustable during assembly and which has a stable structure after assembly.
2. Related Art
In optical fiber technology, wavelength division multiplexing (WDM) couplers are used to combine or separate optical signals having different wavelengths. As WDM couplers are being more broadly applied in the telecommunications, data communications and cable television (CATV) industries, WDM couplers having higher levels of performance and reliability are required.
A WDM coupler comprises two collimator assemblies and a filter member. To minimize transmission losses of light signals, distances between and relative orientations of the two collimator assemblies and the filter member have to be fixed precisely.
Referring to FIG. 4, a conventional WDM coupler disclosed in U.S. Pat. No. 6,343,166 comprises two collimator assemblies (not labeled), a filter 624, and a filter holder 626. The filter 624 is partially received in the filter holder 626 to form a filter subassembly (not labeled). An aperture 627 within the filter holder 626 extends between the filter 624 and lens 622. The filter subassembly is aligned with the two collimator assemblies to transmit light signals having a preselected wavelength and to reflect all other. However, the filter holder 626 has a predetermined structure and the aperture 627 has a predetermined length, which limits readjustments of the distance between the filter 624 and the lens 622.
Another conventional WDM coupler is disclosed in U.S. Pat. No. 6,282,339. Although the disclosed coupler also has two collimator assemblies and a filter, the filter is directly attached to a face of a collimating lens using adhesive. The adhesive can act as a contaminant between the lens and filter, which can cause problems.
An improved WDM coupler which is efficiently adjustable during assembly and which has a stable structure after assembly is desired to overcome the above-mentioned problems.